U.S. patent number 5,181,788 [Application Number 07/657,247] was granted by the patent office on 1993-01-26 for ribbon saving control mechanism.
This patent grant is currently assigned to BanTec, Inc.. Invention is credited to James R. Ingram, Jr., Joel Y. Lin, Thomas J. Norman, Jr..
United States Patent |
5,181,788 |
Norman, Jr. , et
al. |
January 26, 1993 |
**Please see images for:
( Certificate of Correction ) ** |
Ribbon saving control mechanism
Abstract
A ribbon control mechanism for a serial encoding device is
provided to conserve the usage of single-strike ribbon consumed
during printing. The mechanism includes a ribbon transport
mechanism and means for signaling the transport mechanism to
reverse the ribbon between documents to position the ribbon for
printing in unspent ribbon.
Inventors: |
Norman, Jr.; Thomas J.
(Richardson, TX), Ingram, Jr.; James R. (Dallas, TX),
Lin; Joel Y. (Denton, TX) |
Assignee: |
BanTec, Inc. (Dallas,
TX)
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Family
ID: |
27361437 |
Appl.
No.: |
07/657,247 |
Filed: |
February 15, 1991 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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338868 |
Apr 17, 1989 |
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20444 |
Mar 2, 1987 |
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Current U.S.
Class: |
400/232;
400/225 |
Current CPC
Class: |
B41J
33/388 (20130101); B41J 33/44 (20130101) |
Current International
Class: |
B41J
33/388 (20060101); B41J 33/44 (20060101); B41J
33/14 (20060101); B41J 033/51 () |
Field of
Search: |
;400/231-233,218,223,224,225,227 ;101/336 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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67494 |
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Apr 1983 |
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JP |
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207276 |
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Nov 1984 |
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JP |
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Primary Examiner: Wiecking; David A.
Assistant Examiner: Kelley; Steven S.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This is a continuation of prior co-pending application Ser. No.
07/338,868 filed on Apr. 17, 1989, which is a continuation of prior
co-pending application Ser. No. 07/020,444, filed Mar. 2, 1987,
both now abandoned.
Claims
We claim:
1. An encoding apparatus for depositing discrete series of
characters on documents transported through the apparatus,
comprising:
a document transport mechanism for engaging a document and
transporting it through the encoding apparatus along a document
pathway;
a die set fixed to the apparatus and having characters extending
from a surface thereof along a portion of one side of the document
pathway;
a plurality of striking elements fixed to the apparatus in opposing
relationship to the characters of the die set on the other side of
the document pathway and disposed for striking documents in the
document pathway in response to control signals;
a single-strike, ink-bearing ribbon interposed between the striking
elements and characters of the die set; drive means selectively
transporting a portion of the ribbon along the document pathway
either in the same direction and at the same speed as the document
transported through the apparatus or in a reverse direction with
respect to the document transport direction;
means responsive to the encoding of the chronologically last
character in a particular series of characters for determining a
length of ribbon to be transported in said reverse direction before
a subsequent series of characters is encoded;
means controlling the drive means to stop and reverse the drive
means after the chronologically last character in the particular
series of characters is encoded a linear distance substantially
equal to said determined length, the ribbon being reversed to a
ribbon position where encoding of the subsequent series of
characters will begin in a portion of the ribbon substantially
adjacent to a portion of the ribbon consumed in printing the first
series of characters; and
said drive controlling means reverses the ribbon a variable reverse
distance after printing the particular series of characters on a
document, said drive controlling means determining the reverse
distance by the formula:
where String Length is the total number of characters in the
particular series of characters printed,
Striking element Number is a number between one and the total
number of striking elements used in printing the particular series
of characters, and
Character Position Number is a number between one and the total
number of characters in the particular series of characters.
2. In a printing device for discrete documents continuously moving
through said device, where each document passes between at least
one fixed character die set on one side of the document and at
least one fixed set of striking elements on the other side of the
document, the document and a single-strike, ink-bearing ribbon
moving through the character die set and striking elements in
unison during printing, and the striking elements being sequenced
in response to control signals from a control computer to print at
least one desired series of characters on the document, the
improvement comprising:
drive means for advancing and reversing the ribbon in response to
control signals from the control computer;
the control computer including means responsive to the encoding of
the chronologically last character in a particular series of
characters for determining a length of ribbon to be reversed before
a subsequent series of characters is encoded and means for
signaling the drive means to reverse the ribbon a linear distance
substantially equal to said determined length to position the
ribbon for printing in the portion of unspent ribbon substantially
adjacent to a portion of spent ribbon; and
said control computer activates said drive means to reverse the
ribbon a variable distance after printing the particular series of
characters on a document, said control computer determining the
reverse distance by the formula:
where String Length is the total number of characters in the
particular series of characters printed,
Striking Element Number is a number between one and the total
number of striking elements used in printing the particular series
of characters, and
Character Position Number is a number between one and the total
number of characters in the particular series of characters.
Description
TECHNICAL FIELD
This application relates to ribbon control mechanisms for document
encoders and more particularly to a ribbon control mechanism
including reversible drive apparatus for a document encoder using a
single-strike ribbon.
BACKGROUND ART
Document encoders which are well known in the art typically fall
into two general categories. The first category of encoders
includes those encoders which utilize a step function to position
the document to be encoded at a particular point. Such encoders
function in a manner typically associated with typewriters or other
mechanical printers and are not generally compatible with high
speed document processors.
A second category of document encoders which is capable of encoding
continuously moving documents is nonetheless incompatible with
modern financial document processors. The second category of
encoders includes laser printers and ink jet printers. While these
two types of encoders are capable of encoding a moving document,
the magnetic ink required for use with financial documents such as
checks is incompatible with current ink jet technology.
It is known in the art to print across a document in horizontal
motion, sometimes referred to as horizontal "on the fly" printing.
Printing "on the fly" may be accomplished by providing a number of
fixed hammers and a corresponding set of fixed character dies,
through which a document and an ink ribbon are transported in
unison while the hammers are activated to print a sequence of
characters on the document. The printing of documents "on the fly"
has been used with great success in the encoding of financial
documents, such as checks, in high speed encoding systems such as
the one shown in U.S. Pat. No. 4,492,161 issued to the assignee of
the present application, the disclosure of which is incorporated
herein by reference.
In the prior art "on the fly" financial document encoders, magnetic
ink ribbons are used to encode the documents with magnetic
characters. Such magnetic ink ribbons are typically single-strike
ribbons, that is, the magnetic ink associated with each character
is totally removed from the ribbon during the printing of that
character, and the same section of ribbon cannot be used a second
time. In the prior art encoders, the ribbon control mechanism
provides for transport of the ribbon in one direction only, with
the ribbon transport being activated to transport the ribbon in
unison with a financial document in the apparatus by the sensing of
the leading edge of the document just before the document enters
the print zone between the hammers and die. Specifically, an
optical sensor is provided to sense the leading edge of the
document and is located directly adjacent the entrance to the print
zone. The ribbon transport is then deactivated in the prior art
mechanism when the encoding process on a document is finished.
The prior art ribbon transport is deactivated once the last
character in a series of characters, in time, is struck. It will be
understood from the disclosure of the assignee's aforementioned
prior patent that the character physically located last in a series
of characters on a document is not necessarily the last character
to be struck in time. The chronological sequence of character
strikes will be dependent not only on the position of the character
on the document but also the position of the character on the die
set. As a result, when the last character is struck, a gap of
unspent ribbon remains in the die between the entrance to the print
zone and the last character. This portion of unspent ribbon is not
used in printing the next document to enter the print zone, because
the ribbon transport will be activated as the next document enters
the print zone.
The gaps of unspent ribbon between spent portions represents a
substantial wastage of ribbon. At a typical wastage rate of 50%,
the typical customer encoding one million documents per month could
realize a substantial savings if the amount of ribbon wastage could
be controlled, thus, a need presently exists for a ribbon control
mechanism that eliminates the gaps of unspent ribbon in an "on the
fly" printing apparatus.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an
improved document encoder.
It is another object of the present invention to provide an
improved document encoder that is capable of encoding continuously
moving documents.
It is yet another object of the present invention to provide an
improved document encoder that is capable of encoding continuously
moving documents utilizing magnetic ink.
The foregoing objects are achieved as is now described. Documents
are transported between a plurality of fixed dies and a plurality
of electronically controlled hammers. A magnetic ink bearing ribbon
is interposed between the documents and the fixed dies and is
transported at the same velocity as the documents. As the documents
traverse the plurality of fixed dies, the electronically controlled
hammers are cycled, in a selected sequence and at selected
positions. In those applications in which the cycle time of the
electronically controlled hammer is too slow to allow identical
encoding in adjacent positions, a second plurality of fixed dies
and associated electronically controlled hammers may be located
adjacent to the first plurality or interspersed among the first
plurality of fixed dies.
The present invention solves the problem of wasted unspent ribbon
by providing a ribbon control mechanism for reversing the ribbon
between documents to eliminate gaps of unspent ribbon between spent
portions. The portion of the ribbon that is unspent after an
encoding operation is salvaged by backing up the ribbon to a point
where only spent ribbon is in the print zone and the unspent
portion begins at the entrance to the print zone. Because a
variable amount of unspent ribbon is generated depending on the
sequence of characters, in the preferred embodiment the control
computer is used to calculate the exact amount that needs to be
reversed. In a simplified embodiment, the ribbon is continued to be
fed with the document until the last character of the last printed
field exits the print zone. Unspent ribbon then exists in the print
zone for the entire length of the die. The ribbon is then reversed
for the length of the die. Ribbon transport apparatus capable of
rapidly accelerating the ribbon in both forward and reverse
directions is provided by using vacuum columns in the ribbon supply
and takeup mechanisms. A capstan moves the ribbon in the print zone
between the vacuum columns.
BRIEF DESCRIPTION OF THE DRAWINGS
The novel features believed characteristic of the invention are set
forth in the appended claims. The invention itself; however, as
well as a preferred mode of use, further objects and advantages
thereof, will best be understood by reference to the following
detailed description of an illustrative embodiment when read in
conjunction with the accompanying drawings, wherein:
FIGS. 1A and 1B form a general block diagram of a document
processing system incorporating the present invention;
FIG. 2 depicts a diagrammatic view of the document transport of a
document processing system incorporating the present invention;
FIG. 3a depicts a block diagram of the encoder of a document
processing system incorporating the present invention;
FIG. 3b depicts a diagrammatic view of an encoder apparatus of the
type to be improved by the present invention;
FIG. 4 is a diagrammatic view of improved encoder apparatus
incorporating the present invention;
FIG. 5 is an elevation view of a die set used in conjunction with
the invention;
FIG. 6 is a partial view of a corner of a document with MICR
coding; and
FIGS. 7a and 7b are views of spent ribbons illustrating the
advantages of the present invention.
DETAILED DESCRIPTION
Referring to FIGS. 1A and 1B, there is depicted a general block
diagram of the various subsystems comprising a document processing
system.
The document processing system is controlled by digital computer
100. Digital computer 100 coordinates the storage and retrieval of
digitized document images and associated data which are stored, in
the disclosed embodiment, in magnetic disk storage. Disk controller
102 controls the actual access of digitized document images via
disk drives 104, 106, and 108. Additional data, accounting
information or program data may be accessed by digital computer 100
through tape controller 110 which controls magnetic tape drives 112
and 114. It will be appreciated by those skilled in the art that
disk controller 102 and tape controller 110 may control an
increased or decreased number of disk or tape drives, as a matter
of design choice. Digital computer 100 may selectively access
either magnetic disk storage or magnetic tape storage through
channel selector 116.
Digital computer 100, in the embodiment disclosed, interfaces with
a local operator via the computer I/O bus and printer interface
118. Printer interface 118 controls line printer 120. In alternate
modes of operation wherein remote communication with digital
computer 100 is desired, a modem and appropriate interface
circuitry may be utilized.
Digital computer 100 also controls the operation of laser printer
subsystems 124, through laser printer interface 122. Laser printer
subsystem 124 is utilized to provide hard copy of selected digital
images and may be utilized to generate account statements, billing
statements, or other correspondence comprising any combination of
alphanumeric characters and images.
Video terminal subsystem 136 is utilized in the document processing
system to provide a real time, controllable video display of
selected documents and alphanumeric information. The display is
utilized to facilitate processing of information on each document.
Digital computer 100 controls the operation of video terminal
subsystem 136 through buffer interface 144 and synchronous data
link control master 146. A plurality of video display terminals may
be utilized with each SDLC master.
High speed transport subsystem 148 is utilized to transport
individual documents through image capture stations, machine
readers, encoders and sorters. A plurality of high speed transports
may be utilized within each document processing system, thereby
increasing the capacity of an individual system. High speed
transport system 148 is controlled utilizing buffer interface 156
and synchronous data link control master 158. High speed transport
system 148 will be explained in greater detail with respect to FIG.
2.
Digital image data obtained from the digital camera or cameras
installed in each high speed transport is transferred to camera
interface 160. Camera interface 160 is utilized to couple the image
data to digital image compactor 162. Digital image compactor 162 is
utilized to remove any redundancies contained in a selected image
and to encode the remaining data. The thus compacted digital image
will require substantially less storage space in the document
processing system. The compacted image data may be transferred to
storage via multiplexed direct memory access 164 and multiplexed
direct memory access 166. Two direct memory systems are utilized in
order to provide compatible interfaces between the local X bus and
the direct memory access interface bus of digital computer 100.
Retrieval and display of a compacted digital image may take place
in several ways. A compacted image is transferred to the local X
bus via direct memory access 164 and direct memory access 166. The
compacted image is applied to digital image expander 168. The
redundancies present in the original image are restored and the
subsequent image is transferred via X bus distributor 170 or X bus
distributor 172 to either laser printer subsystem 124 or video
terminal subsystem 136 for reproduction of a hard copy or an
electronic image.
Digital Computer
The document processing system utilizes a digital computer 100,
FIG. 1A, to control the operation of the system and coordinate the
storage and retrieval of document images. In one embodiment digital
computer 100 may be a Series 3200 minicomputer, manufactured by the
Perkin-Elmer Computer Systems Division of Oceanport, N.J.
The Model 3242 minicomputer utilizes 32-bit architecture and a
32-bit operating system. The main memory storage contains 1536
kilobytes of 150 nanosecond MOS memory. Supplementing the
computer's main memory store are disc drives 104, 106 and 108 (FIG.
1B), Model 9775 manufactured by Control Data Corporation of
Minneapolis, Minn., and tape drives 112 and 114 (FIG. 1B), Model
TPAC 4516, manufactured by Perkin-Elmer of Oceanport, N.J.
Digital computer 100 can also include a rechargeable battery backup
system (not shown) to sustain the main memory in the event of a
power failure. Digital computer 100 can utilize a battery rated at
320 megabyte-minutes, which is capable of maintaining the memory
integrity of 16 megabytes for twenty minutes.
Document Transport
Referring now to FIG. 2, there is depicted a diagrammatic plan view
of document transport 200. Document transport 200 is a specially
built transport which may be modified to include additional
equipment or to exclude undesired capabilities. The transport
constructed and depicted in FIG. 2 utilizes high speed endless
belts which are driven by pinch rollers in the manner well known in
the art. The pinch rollers are driven by synchronous AC motors at a
nominal speed of 52 inches per second in the disclosed embodiment.
Sections of the transport may be driven at different speeds in a
manner described below.
Documents are loaded into document transport 200 by means of
document hopper 202. Single documents are loaded from document
hopper 202 via feed drum 204. The documents are then passed along
document transport 200 between rollers and the endless belts (not
shown). The first section of document transport 200, reader section
206, includes an optional character reader 208 and a magnetic ink
character reader 210.
The next section of document transport 200 is encoder section 212.
Encoder section 212 includes hammer bank assembly 214 and die and
ribbon assembly 216 and is utilized to encode selected documents
with selectable indicia, while the document is traversing document
transport 200. The operation of the encoder section will be
explained in greater detail with reference to FIGS. 3a, 3b, 4, 5,
6, 7a and 7b.
Section 218 of document transport 200 is the endorser section.
Endorser section 218 contains ink jet printers 220 and 222 and
endorser 224. Ink jet printers 220 and 222 are standard state of
the art ink jet printers that may be utilized, in the disclosed
embodiment, to print selected indicia upon each document which
passes through document transport 200. The selected indicia may be
utilized to assist in audit trail functions or in any other
function desired. Endorser 224 is utilized to endorse documents
such as checks.
The next section in document transport 200 through which each
document is transported is camera section 226. Camera section 226
contains, in the embodiment disclosed, two digital video cameras,
228 and 234 and two illumination sources, 230 and 232. Each
document which passes through camera section 226 is scanned on both
sides utilizing video cameras 228 and 234.
The penultimate section of document transport 200, microfilm
section 236, contains a microprocessor controlled microfilm
recorder 238. Microfilm recorder 238 is utilized to provide hard
copy of selected documents which have been processed by the system
of the invention.
The final section of document transport 200 is stacker section 240.
Stacker section 240, in any manner well known in the art, sorts the
documents processed through document transport 200 into one of
several pockets. The number of pockets is, of course, a design
choice wholly dependent upon the application desired.
As those skilled in the art will appreciate, the modularity of
design employed in document transport 200 will allow great
flexibility in many applications. Whole sections of document
transport 200 may be deleted or rearranged to permit a wide variety
of custom applications. Further, the number and type of devices
within each module may be increased or decreased as a matter of
design choice.
Encoder
With reference now to FIG. 3a, there is depicted a schematic view
of an encoder 300. An important feature of the system is the
ability to encode continuously moving documents. Document encoder
300 is capable of encoding documents which are continuously moving
at the rate of the overall document processing system hereof.
Document encoder 300 utilizes, for example, two identical
electromagnetic hammer banks, hammer bank 302 and hammer bank 304.
It will be apparent, however, upon reference to the foregoing
explanation, that a fewer or greater number of hammer banks may be
utilized in systems wherein slower or faster transport speeds are
desired. Hammer banks 302 and 304 are electromagnetic hammers such
as part no. CCE-05-306 manufactured by Dataproducts, Woodland
Hills, Calif. Each hammer bank is controlled by a hammer driver. In
the disclosed embodiment, hammer driver 306 controls hammer bank
302 and hammer driver 308 controls hammer bank 304. Hammer power
supply 310 provides operating power for all hammer drivers and
hammer banks.
Positioned opposite each hammer bank is an appropriately encoded
die. The selection of characters utilized in a particular
application is strictly a design choice and may include OCR
characters. MICR characters or any other desired character pattern.
The illustrated embodiment includes two substantially identical die
sets, die set 312 and die set 314. However, as a matter of design
choice, a single die set may be utilized. Also included in the
illustrated embodiment is microprocessor control 316, which
provides control signals to hammer drivers 306 and 308 in response
to signals from optical sensor 318. Optical sensor 318 is utilized
to detect the presence of a document along document path 320.
FIG. 3b depicts a partially diagrammatic view of the major
components of document encoder 300. As explained above, hammer
banks 302 and 304 selectively strike portions of die sets 312 and
314, upon receipt of control signals generated by a microprocessor
control 316 (see FIG. 3a), in conjunction with an item presence
signal generated by optical sensor 318.
Ribbon mechanism 322 (FIG. 3a) is shown in greater detail in FIG.
3b and includes a ribbon supply reel 324, ribbon takeup reel 326,
ribbon tensioning arms 330 and 332 and ribbon capstan 338. Ribbon
supply reel 324 provides a fresh supply of magnetic ink ribbon 340.
Such magnetic ink ribbons are typically single strike ribbons, that
is to say the magnetic ink associated with each character is
totally removed from the ribbon during the printing of that
character and further attempts to print utilizing the same section
of ribbon 340 will result in invalid magnetic signatures.
Therefore, it is necessary to advance magnetic ink ribbon 340 after
each character is printed, and it is advantageous, from an economy
standpoint, to advance ribbon 340 only while a document is present
in encoder 300. This is accomplished utilizing ribbon capstan 338
which is electronically controlled by microprocessor control 316
during those periods when a document is detected by optical sensor
318. Ribbon 340 is driven by ribbon capstan 338 at the same speed
as documents on the transport. The rapid acceleration of ribbon 340
to transport speed is accomplished without damage to ribbon 340
utilizing ribbon tensioning arms 330 and 332. Ribbon tensioning
arms 330 and 332 are pivotally mounted at point 342 and resiliently
biased utilizing springs 334 and 336. A rapid acceleration of
ribbon 340 is then absorbed by ribbon tensioning arms 330 and 332
until ribbon supply reel 324 and ribbon takeup reel 326 can
compensate.
In operation, encoder 300 utilizes two character sets to compensate
for the duty cycle of the hammer bank utilized. Each individual
hammer within hammer banks 306 and 308 has a duty cycle of
approximately 0.004 seconds. Document encoding standards for MICR
require individual characters to be encoded approximately one-eight
inch apart, one-tenth inch spacing for OCR. At a nominal transport
speed of 52 inches per second, a document will travel one-eighth
inch in approximately 0.0024 seconds. It should therefore be
apparent that with a duty cycle of 0.004 seconds, a single hammer
and die combination will be unable to repetitively strike a single
character at one-eight inch intervals. Thus, the use of multiple
hammers and substantially identical character sets will allow full
encoding at the present duty cycle. Consider a possible worse case
analysis, a desired encoding of eight consecutive identical
characters. Those skilled in the art will appreciate that a single
hammer and die will be able to encode alternate digit positions at
the stated speed of operation. The second group of hammers and
characters allows encoder 300 to fill in the missing digits. More
specifically, hammer bank 306 and die set 312 may encode the odd
digit positions in a desired field, and hammer bank 308 and die set
314 may encode the even digit positions. Thus, it should be
apparent that increased or decreased transport speeds may be
accommodated by utilizing a greater or fewer number of hammer banks
and die sets, without requiring a faster duty cycle for individual
hammers. It should also be apparent that since certain portions of
a particular digit field may be encoded by one hammer bank while
other positions may be encoded by a second hammer bank, it will be
advantageous to maintain ribbon 340 at the same speed as the
documents passing through encoder 300. By so doing, the used
portions of ribbon 340 associated with a particular character will
maintain its relative position directly above that particular
character on the document.
Referring now to FIG. 4, an improved ribbon control mechanism
incorporating the features of the present invention includes ribbon
410 in encoding mechanism 412 for encoding characters upon
documents 414 and 416 transported along a document pathway
represented by arrow 418. Ribbon 410 is selectively transported
through encoding mechanism 412 by means of a ribbon control
mechanism that includes feed reel 420, feed vacuum column 422,
guide rollers 424 and 426, capstan 428, takeup vacuum column 430
and takeup reel 432. Documents such as documents 414 and 416 are
transported by means of a document transport system including belts
434.
The document pathway includes print zone 436 between a plurality of
hammers 438 and die set 440. Hammers 438 are fixed to encoding
apparatus 412, as is die set 440, which is fastened to encoding
mechanism 412 by way of screws 442 and base 443.
Documents 414 and 416 are illustrated as being bank checks.
Typically, bank checks include pre-printed information along the
lower edge thereof in zones 444 and 446 of document 414. A zone 448
is provided for subsequent encoding of such information as the
amount of the check. Obviously, the amount of each check is
variable, and encoding apparatus 412 encodes the documents 414 and
416 with information concerning the amount of the checks in field
448. Document 416 is shown subsequent to encoding information 450.
It will be appreciated that encoding apparatus 412 is specially
adapted for depositing variable sequences of characters on discrete
documents transported through the apparatus at high speed.
Referring now to FIG. 5, die set 440 includes a series of reverse
characters 460 extending from surface 462. Surface 462 is not
visible in FIG. 4, but it will be understood that a document
entering print zone 436 will first encounter character 464 and last
encounter character 466. Thus, index numerals 468 range from "1" to
"24" and correspond to the position of the characters on the die
set. Thus, for example, the character designated by reference
numeral 470 is characterized by the index number "7" because it is
the 7th character from character 464. For ease of reference, the
index number between "1" and "24" used to describe the position of
the character will be referred to as the "Striking Element Number"
of that character.
Referring now to FIG. 6, the lower right-hand corner of document
416 includes character sequence 450 as previously described in
connection with FIG. 4. A typical number of characters in sequence
450 would be twelve, and the index numbers 484 between "1" and "12"
can be used to describe the position of the characters on the
document. In sequence 450, the character designated by reference
numeral 480 is described by the index number "1" whereas the
character designated by reference numeral 482 is described by the
index number "12". For ease of reference, the index number between
"1" and "12" used to describe a character in sequence 450 shall be
referred to as the "Character Position Number" of that character.
Sequence 450 itself can be described in terms of the total number
of characters in the sequence, in this example twelve, and this
number may be referred to as the "String Length". Document 16
includes leading edge 486, which is the first portion of the
document to enter print zone 436.
Referring now to FIGS. 7a and 7b, ribbon portion 500 includes spent
portions 502 separated by a wide portion of unspent ribbon 504.
Ribbon portion 500 is illustrative of the ribbon used in the prior
art apparatus where the ribbon transport system moved the ribbon
only in the forward direction, stopping the ribbon between
documents. By way of contrast, ribbon portion 506 includes spent
portions 508 separated by relatively narrow unspent portions 510.
The width of portions 510 is a matter of design choice and can be
eliminated completely if desired.
In operation, documents such as documents 414 and 416 are printed
while they are in horizontal motion, known as "on the fly"
printing. Documents are transported along the document pathway
indicated by arrow 418 through print zone 436, where hammers 438
are sequenced according to control signals to print a desired
sequence of characters on the document. By referencing leading edge
486 of the document to the die set and by knowing the document
speed as well as the desired character to be printed in each
desired character position, through use of a control
microprocessor, the desired characters can be printed within
allowed tolerances in the desired spaces "on the fly" as the
document passes through the print zone.
An unused portion of the ribbon must be present between a hammer
and a die character at the instant that the hammer is fired to
strike the die. Thus, the ribbon and the document to be printed
must move in unison through the print zone. After the last
character hammer is fired, in time but not necessarily in position,
the ribbon can stop while the document proceeds through the print
zone. Because the last hammer in time to fire is usually not the
first hammer in position to fire, there is usually a portion of the
ribbon left unspent which can be salvaged by backing up the ribbon
to a point where only spent ribbon is in the print zone and unspent
ribbon begins at the entrance to the print zone.
Bidirectional capability of the ribbon control mechanism is
provided by enabling capstan 28 to rotate in either the forward or
reverse direction. In the preferred embodiment, a stepper motor is
used in conventional fashion to advance and reverse the capstan in
a highly controlled fashion. Stepper motors are also used in
conventional fashion to drive feed reel 420 and takeup reel 432.
Because the ribbon in the print zone is constantly being
transported in forward directions as well as variable reverse
directions, the operation of the stepper motors which drive feed
reel 420 and takeup reel 432 is asynchronous with respect to the
stepper motor which drives capstan 428. Conventional MICR ribbon is
highly stretchable, so the rapid accelerations required by the
ribbon control mechanism are enabled by using vacuum columns 422
and 430. Vacuum columns are known in the art of computer tape
control mechanisms, and in conventional fashion vacuum columns 422
and 430 are buffered with photocells. As will be understood by
those skilled in the art, the vacuum in vacuum columns 422 and 430
is sufficient to generate sufficient forces on each side of the
capstan 428 to move the ribbon in a controlled manner.
The amount of ribbon reversal can be controlled in either of two
ways. Since the goal is to reverse the ribbon to the point where no
unspent ribbon remains in the print zone, the worst case in terms
of amount of unspent ribbon in the print zone would occur when the
character on the document Character Position Number "12" (FIG. 6)
is struck by the character in the die set at Striking Element
Number "24" (FIG. 5). In this worst case, unspent ribbon would fill
the print zone for substantially the length of die set 462. Thus, a
simple way to control ribbon reversal is merely to assume the worse
case each time a document is printed, stop the ribbon transport as
the printed field leaves the print zone, and reverse the ribbon an
amount substantially equal to the length of the character die set.
A disadvantage of this approach is that the ribbon is moved a
greater distance in most cases than is actually required, allowing
more opportunity for particles to be scraped off which can result
in voids in the ink layer or extraneous ink on the documents.
The preferred way to control ribbon reversal is to calculate the
precise amount of unspent ribbon remaining in the print zone when
the last character in time is struck and driving the capstan in
reverse a sufficient amount to leave only spent ribbon in the print
zone. Thus, the amount of reversal is a calculated amount based on
the printing pattern of the just-printed document. The variable
reverse distance can be calculated for each sequence by the
following formula:
as those terms have been defined above. Thus, for each sequence,
the Striking Element Number and Character Position Number for each
character to be printed are summed, and the highest sum (MAX) is
determined. It will be understood that the sum of the Striking
Element Number and Character Position Number determines the
chronological sequence in which given characters in a sequence will
be struck. The maximum sum of these two numbers is then reduced by
the amount of the String Length, and the Reverse Distance remains.
Thus, it can be seen that the Reverse Distance is an amount
corresponding to the amount of unspent ribbon between the die set
and hammers when the last character in time is struck.
A document may have several sequences in which case the ribbon may
be reversed for each sequence or any combination of adjacent
sequences.
Whereas the present invention has been described with respect to
specific embodiments thereof, it will be understood that various
changes and modifications will be suggested to one skilled in the
art and it is intended to encompass such changes and modifications
as fall within the scope of the appended claims.
* * * * *